Search

The Al alloy and carbon fiber reinforced polymer (CFRP) hybrid structures, incorporating the performance advantages of the two materials, have been attracting more attention in high-end manufacturing fields. In the current investigation, the flat friction spot joining (FSJ) was employed in joining the AA6061-T6 alloy and CFRP sheets. The significance of temperature distribution in influencing joint quality was highlighted through analyzing interface microstructural features, weld defect formation as well as fractography. To understand the role of thermal energy generation and conduction in the process comprehensively, a 3D thermal-mechanical coupling finite element model was established. The interfacial temperature was characterized by an uneven distribution behavior due to the inhomogeneous heat distribution. The peak temperatures on the top surface and Al alloy to CFRP interface at 1500 rpm rotational speed with 0.1 mm/s plunging speed were 498 °C and 489 °C, respectively. The peak interface temperature was reduced to 286 °C at 250 rpm, which produced an extremely small melted area. Compared with the plunging speed, rotational speed was found to be the predominant parameter for determining the joint property, which could be optimized to simultaneously realize the avoidance of thermal decomposition of CFRP, the sufficient melting duration time, and the wide enough melted area. Simulated thermal histories and melted area profiles were in agreement with experimental ones. The findings could be utilized to provide some feasible guidance for process optimization of dissimilar FSJ of metals and composites.

s Feed-water valves (FWVs) are used to regulate the flow rate of water entering steam generators, which are very important devices in nuclear power plants. Due to the working environment of relatively high pressure and temperature, there is strength failure problem of valve body in some cases. Based on the thermo-fluid-solid coupling model, the valve body stress of the feed-water valve in the opening process is investigated. The flow field characteristics inside the valve and temperature change of the valve body with time are studied. The stress analysis of the valve body is carried out considering mechanical stress and thermal stress comprehensively. The results show that the area with relatively high-velocity area moves gradually from the bottom of the cross section to the top of the cross section with the increase of the opening degree. The whole valve body reaches the same temperature of 250 °C at the time of 1894 s. The maximum stress of the valve body meets the design requirements by stress assessment. This work can be referred for the design of FWVs and other similar valves.

Manufacture of a transition hybrid coupling from two different steels, medium carbon S355J2 and stainless 316L, has been demonstrated using two different solid-state joining routes, forge welding (FW) and rotary friction welding (RFW). An additional manufacturing route, electron beam welding (EBW), was also employed in investigating its feasibility for such application. Mechanical and microstructure properties of the final components manufactured from the three different routes have been compared. Finite element (FE) analysis was utilised to determine optimal geometries for the FW and the RFW preform rings and identify optimal parameters for both processes. Of the three manufacture routes, the FW produced an instant diffusion-like bond with a single forging stroke on a 2100T screw press with the thinnest weld interface and most uniform hardness distribution at either side of the joint. The RFW part, manufactured on a 125T RFW machine, also exhibited a very thin weld interface, yet slightly thicker compared to the FW case, with small variations in the hardness distribution at either side. The EBW produced markedly thicker weld interface compared to the two solid-state routes. The EBW part exhibited significant variation in hardness distribution across the weld exhibiting peak hardness in the weld indicating requirements for a post-weld heat treatment (PWHT). Both the FW and the RFW process routes exhibited very uniform micro-hardness and microstructures across the weld interface in contrast with the EBW process in as-manufactured condition.

A theoretical model is developed to investigate the influence of external mean flow on sound transmission loss (STL) through composite sandwich panels filled with porous materials. The equations of the motions for the composite laminate plates are established by adopting the first-order shear deformation theory. The porous materials in between the sandwich structures are characterized by an equivalent fluid model. Employing the fluid-structure coupling condition, the displacement continuity at fluid-structure interfaces is guaranteed. To validate the proposed theoretical model, a comparison among the present theoretical predictions, the existing theoretical and experimental results are executed, with overall agreements achieved. A systematical investigation is carried out to explore the influences of the external mean flow, incidence angle and laminate scheme on the coincidence frequency and sound transmission loss of the sandwich structures. This work provides a helpful guideline for the vibroacoustic design of composite sandwich structures.

Monoblock prestressed concrete sleepers are the most dominant type of sleepers in ballasted railway tracks. As such, it is important to provide optimized designs to the concrete sleepers and the associated fastening systems to ameliorate railway safety and to save both capital and maintenance funds. Therefore, a three-dimensional finite element railway model was created and verified. The response of both concrete sleepers and fastening components to coupling vertical and lateral loading was quantified. Such loading form typically occurs at horizontal railway sections causing damage to the railway track components. The influences of the sleeper spacing, elastic modulus of the rail pad, and friction coefficient at the contact surfaces of the rail and sleeper with the rail pad under varied lateral loadings were investigated. The interaction influence between parameters was thoroughly discussed. Among the studied parameters, the finite element model outcomes showed that the elastic modulus of the rail pad and the coefficient of friction are the most critical parameters with respect to the lateral load path and the local response of concrete sleeper and fastening system, especially at high lateral loadings. By using a relatively soft rail pad (elastic modulus = 100 MPa), the concrete material remained below the compressive and tensile fatigue limits even under high lateral loadings provided that the coefficient of friction remains limited to 0.3. By contrast, for a given lateral to vertical loading ratio, a continuous increase in the developed stresses of the concrete material and rail pad was detected as the elastic modulus changed from 100 MPa to 2000 MPa and the coefficient of friction increased from 0.3 to 0.9. The influence of sleeper spacing on the behaviour of railway tracks is only tangible on the distribution of the vertical wheel load. Lastly, the peak stress magnitudes of the ballast bed could be increased by 50% as the lateral to vertical loading ratio reached 0.6 compared to the case where the lateral load is absent. The experience gained from this article would help to formulate specific recommendations to improve the design of concrete sleepers, fastening systems, and ballast bed.

The unsatisfactory solar light absorption of WO3 and poor charge separation of BiVO4 are main limits for their use in photoelectrochemical (PEC) water oxidation. Coupling WO3 with BiVO4 has been considered as a feasible way to improve PEC performance by taking complementary advantages of them. In this work, we obtained nanoflake-structured WO3 by hydrothermal growth with post-annealing. The effect of process variables on morphology and resultant performance were investigated. Electrodeposition growth was utilized to deposit BiVO4 onto WO3 forming WO3/BiVO4 heterojunction thin films. Porous BiVO4 with wormlike morphology was tightly coupled and well-distributed onto WO3 nanoflakes. The optimized best-performing WO3/BiVO4 photoanode exhibits higher photocurrent density than that summation of bare WO3 and BiVO4 over entire range of applied potential. This enhancement is mainly attributed to the effective charge separation at WO3/BiVO4 interface, which is confirmed through electrochemical impedance spectra (EIS) measurements, respectively. Our work provides a referable approach for the growth of WO3/BiVO4 heterojunction photoanode with enhanced PEC performance.

Geometric parameters present varying degrees of coupling effects on different performance indexes including slip resistance, preload force, and steel plate stress of friction high-strength bolts, resulting in mutual restraint relationships among these indexes. Design parameters and performance assessing indicators, in the current code, are relatively simple mentioned, which have few relevant investigations on the influences of different parameters to the mechanical performance of high-strength bolts by a more comprehensive evaluating method. This paper has systematically studied the influences of geometric parameters on the overall performance of friction-type high-strength bolts through four performance evaluation indexes based on finite element method and multi-objective optimization technology. The obtained results showed that the preload force loss of bolt slip was maintained within 5% and part dimension had a major impact on the stress distribution performance of bolt connection. The performance indexes of slip resistance, preload force, steel plate stress, and friction stress were mainly affected by cover plate thickness, middle plate thickness, hole diameter, and nut diameter. From the optimization results, the recommended value range of cover plate to medium plate thickness ratio verified the correctness of existing specifications, and aperture and nut diameter had a narrow value range for the stable performance of high-strength bolts keeping.

Liquid storage tanks are lifeline structures and strategically very important. Heavy damages or even collapse of these facilities subjected to strong earthquakes may cause disastrous consequences. In this paper, the seismic response of a multistage series liquid storage tank was simulated by a finite element method and verified by a scaled-down experiment. The structural flexibility of the tank and the liquid-structure coupling characteristics between the liquid and tank wall were considered in the research. A multimass-block and spring model was employed to be equivalent to the longitudinal vibration of the liquid in the storage tank. The relationships between the connection springs and the elements of the stiffness matrix were explicitly deduced. The seismic response analysis of a four-stage series liquid tank was carried out, and the acceleration response, the stress response of the tank, and the vertical vibration of the liquid were obtained. The experimental results are in good agreement with the simulation results, which verifies the effectiveness of the modeling method in this paper.

Kilometer-deep mines have become the new norm in coal mining. To study the influence of high stress-high ground temperature coupling conditions in deep mines on the oxidative exothermic characteris...

Aiming to study the stray losses and temperature distribution of power transformer ascending flange, a 1:1 test model is built, and the corresponding three-dimensional (3D) finite-element analysis (FEA) model is established. Then the influence of shielding on stray losses distribution is simulated by surface impedance method, and the 4mm copper shielding is selected as the optimized one. Besides, a mixed steel tank lid structure is proposed to limit the maximum loss density in the tank lid. Finally, the temperature field of ascending flange based on magneto-thermal coupling method is simulated, which can provide an effective guidance for allowable lead current and the related optimization.

Drying-induced cracks are an important issue for bi-block ballastless track system consisting of foundation, precast sleepers, and cast-in-place track slab, which not only significantly affects the comfortableness and safety of rapid transit railway but also reduces the service life of ballastless track. In order to explore its damage mechanism, this work presents an evolution model of relative humidity (RH) in the CRTS I bi-block ballastless track system by considering the actual construction sequence and environmental conditions to simulate the crack propagation induced by nonuniform RH field. Firstly, based on the node coupling technique, a three-step transfer process of RH is designed to separately investigate the influence of the construction sequence on the early humidity field in the foundation, sleepers, and cast-in-place track slab, and then the nonuniform distribution of early humidity field in the ballastless track system is determined. Subsequently, the formation mechanism of shrinkage crack in the system is analyzed, and the crack propagation path is predicted by using the mixed-mode fracture criterion. The results show that the maximum relative humidity gradient (RHG) appears at the interface between the track slab and the sleeper after concreting the cast-in-place track slab, which causes the maximum principal stress due to the drying shrinkage property of concrete materials. When the maximum principal stress exceeds the tensile strength of the interface, an interface crack will be generated and converted to a splayed crack with an initial angle of about 45° at the sleeper corner, which will be further propagated under the action of drying shrinkage deformation and finally forms a transverse through-wall crack in the track slab. The simulated crack propagation path agrees with the observed one at the site well, and thus the results are beneficial to understand the formation mechanism of through-wall crack in the track slab and further guide the construction design of the bi-block ballastless track system.

With the tremendous development of additive manufacturing technology in recent years, porous infill structures with well-designed topology configurations have been widely used in various physical fields. The porous infill structure may be prone to thermo-mechanical buckling failure under certain extreme thermal conditions due to temperature gradient effects and delicate local details of the porous infill structure.Therefore, a topological optimization design method, which considers the influence of the thermo-solid coupling field on the buckling performance of the porous infill structure, is proposed by using the projection approach merged with the Solid Isotropic Material with Penalization (SIMP) method. Critical buckling load factors obtained with thermal-elastic equilibrium and linear buckling analysis are employed to measure the buckling performance of the structure. Numerical examples show that the proposed method can effectively improve the buckling performance of the porous infill structure under the thermo-mechanical environment.

The accurate determination of coalbed methane (CBM) content is of great significance for its development and utilization as well as for the prevention and control of coal mine gas disaster. In the process of determining CBM content, the coal–gas adsorption system existing in the natural environment is affected by variable temperature–pressure interactions. In this study, methane (CH4) adsorption tests were carried out on coals at different initial equilibrium pressures (IEPs) and in different cooling processes (CPs). The test results indicate that dominant and retrograde adsorption processes existed in the cooling and adsorption processes of the coal sample reaction chamber. During the adsorption process, the temperature variation broke the original adsorption equilibrium, which in turn induced the pressure change in the coal sample reaction chamber, thus resulting in the retrograde adsorption. The intensity of the dominant adsorption increased and then decreased, causing an increase and then a decrease in the retrograde adsorption rate. The commonly used adsorption kinetic models were modified, including the modified pseudo-first-order kinetic model, modified pseudo-second-order kinetic model, modified Bangham kinetic model (MBKM), modified intra-particle diffusion model and modified double exponential model (MDEM). These modified models were used to describe the kinetic characteristics of the dominant process of CH4 adsorption on coals in a variable temperature and pressure environment. The results show that among the modified kinetic models, the MDEM can describe better the kinetic process of the dominant adsorption, followed by the MBKM. The IEP showed positive correlation with the dominant adsorption rate at the initial stage of cooling. For the two CPs (i.e., 293.15–283.15 K and 273.15–263.15 K), the initial adsorption rates at the IEP of 3.83 MPa were, respectively, about 4 and 3 times higher than those at the IEP of 0.72 MPa. The retrograde adsorption process can be described better by a linear model. A peak retrograde adsorption rate existed throughout the adsorption process and increased with increasing IEP. The study of the kinetic process of CH4 adsorption on the coal matrix under the effect of low temperatures and variable pressures will improve understanding of the CH4 adsorption mechanism in a low temperature and variable pressure environment, and provide theoretical support for the development and application of new techniques for CBM content determination.

A full-scale steel portal frame structure, explicitly designed to utilize stressed skin action, was tested to destruction in the early 1970′s. At this time, it was not possible to perform any detailed analysis of such structures; however, using modern computational techniques, detailed Finite Element Models (FEMs) have now been developed. These FEMs show an excellent agreement with the reported test results, including following the nonlinear behaviour to complete collapse. The validated model was then extrapolated into a multi-bay portal structure of more realistic length, and the effect of cladding on the strength and flexibility of the frames was established under both vertical and horizonal loading. Under a distributed vertical load, the cladding initially had little influence although, once the internal frames reached a complete collapse mechanism, the cladding prevented structural collapse until the cladding also failed. However, under horizontal load, the coupling between frames was significant, particularly in the multi-bay case, leading to high forces in the cladding and the structure/cladding interface. The tested frame was stocky and low rise, typical of its time. Today, with taller, more flexible modern frames, stiffer and potentially less robust cladding systems will resist an even more significant proportion of the horizontal load; a warning to the construction industry that parasitic diaphragm action should not be ignored.

To study the effect of acid-heat coupled fracturing on the damage of coal pores and fractures, scanning electron microscope-energy dispersive spectrometry (SEM-EDS), mercury intrusion porosimetry (MIP) were used to analyze. The results of the study show that the acid-heat coupling effect not only changes the microscopic morphology and element composition of the coal sample, but also promotes the formation of a pore-fracture network within the coal, and the connectivity is significantly increased, which is conducive to the diffusion and migration of coalbed methane. The optimum acidification temperature for the experiment is 50 °C. SEM observed that the acid-heat coupling changed the local stress sensitivity of the coal body and weakens the strength of the coal body to form a fracture network. EDS analysis shows that the element distribution on the coal surface changes regularly with the increase of acidification temperature, and the reduction rate of mineral content on the coal surface is highest at 50 °C. MIP and fitting analysis show that the pore parameters of coal samples will increase with the increase of acid-heat coupling temperature, reaching a peak at 50 °C, and the acidification effect will be relatively slow after increasing the temperature. This research is of great significance for exploring the optimal acidification conditions of coal mines, reducing acidizing fracturing costs, and ensuring coal mine safety production.

In order to study the effects of wheel-rail impacts on the fatigue damage of the fastening clips at the rail joints of a high-speed railway, field tests were carried out on the wheel-rail impacts at the rail joints of a high-speed railway in China. On the basis of the track irregularities at the rail joints obtained from field measurements, a nonlinear vehicle-track coupling dynamics three-dimensional (3D) model with consideration of Timoshenko beam elements and a refined finite element model of WJ-8 fastening system were constructed. And combined with the theory of cumulative damage and the method of fatigue analysis, the effects of wheel-rail impact at the rail joints on the fatigue life of fastening clips were analyzed. The results showed that the impacts of the wheel-rail in the joint area caused high-frequency fluctuations in the stress-time curves of the clips, which significantly increased the amplitude of stress cycle and increased a lot of stress cycles, of which the amplitudes were reached at a large level; the clips in the area where a rail joint was located suffered the most serious fatigue damage and had the shortest fatigue life; in the actual operation line, besides the clips in the rail joint area, it is also necessary to be concerned about the fatigue performance of fastening clips near the rail joint area.

In order to improve the prediction accuracy of the theoretical model on steel corrosion degree, the multiple correction coefficient method was used to establish a piecewise constitutive model based...

Notch and size effects show vital influence on fatigue performance of engineering components, which deserve particular attention for ensuring their structural integrity and reliability. In this study, the influences of size effect and stress gradient on effective stress as well as fatigue life were studied. Specifically, the effective stress methods were integrated with stress gradient, by which the relationship between stress gradient and size effect was discussed. In addition, a new stress gradient-based method for notch fatigue analysis was proposed by coupling the Weibull model with critical distance theory. Fatigue tests on Ni-based superalloy GH4169 notch specimens with different sizes were conducted at 650 °C, and experimental data of Al 2024-T351 alloy and low carbon steel En3B notch specimens were utilized for model validation and comparison. Results indicate that the proposed method provides more accurate fatigue life predictions than other effective stress methods.

In order to improve the recovery rate and economic benefit of recyclable support structure, a new type of flexible prefabricated impermeable support structure was introduced in this paper. The steel composite–panel coupling structure was formed. Under the specific geological environment (e.g., urban underground space) with great construction difficulties, the polymer-steel panel composite structure exhibited a good capability of bearing deformation; at the same time, the grouting after the steel structure can prevent the leakage. Finite element model of prefabricated excavation was established for the composite structure. The deformation characteristics of prefabricated structures were achieved. In the calculation model, the thickness of the steel panel was designed to be 3 mm, 6 mm, 9 mm and 12 mm, and the thickness of the polymer impermeable layer was designed behind the steel panel to be 10 mm, 20 mm and 30 mm, respectively, to obtain the maximum deformation of the supporting structure. According to the analysis of the deformation law, it is more suitable to design the thickness of the steel panel to 6 mm and the thickness of the polymer impermeable layer to 20 mm, which can save materials and meet the safety requirements of the project. The in situ layered excavation experiment for the foundation pit was performed, and the effectiveness of the assembled support structure was verified through the strain experiment on the steel panel.

To estimate the multiaxial notch local elastic–plastic strains real timely, an online notch elastic–plastic analytical method is proposed coupling with the modified pseudo stress criterion and Chaboche constitutive model. Moreover, for the Ramberg–Osgood material, the non-proportional cyclic strain hardening can be well considered by the proposed unified online accumulation method of equivalent plastic strain increment. Meanwhile, a rapid and effective simulating algorithm for the proposed online method is provided and verified by the experimental data of TC21 titanium alloy and SAE1070 steel notched specimens. Comparisons show that the simulated results can agree with the measured data quite well under multiaxial irregular loading.

Photovoltaic Thermal (PVT) systems generate hot water and electricity simultaneously. The grade of thermal energy generated by such PVT systems is low, resulting in limited application. To overcome this challenge, the coupling of the PVT system to a secondary flat plate collector (FPC) has been explored in this work. For the system's performance estimation, a 3-D numerical model has been developed for both glazed and unglazed PVT-FPC collector. Based on the numerical model, PVT collectors have been fabricated, and each is then connected in series to a commercially available FPC collector. Experiments conducted on the fabricated PVT-FPC system showed a close match between simulation and experiments. Further, experiments conducted on the unglazed PVT – FPC collector showed a peak outlet water temperature of 60–63 °C at 30 LPH. For the unglazed PVT collector, the peak electrical and thermal efficiency of 16% and 25% is reported respectively, whereas for the FPC collector, the thermal efficiency of 35% is reported. Compared to an individual unglazed PVT collector, 17 °C higher outlet water temperature is reported for the coupled system. Similarly, for the case of glazed PVT-FPC collector, the peak outlet water temperature reported is 65–67 °C at 30 LPH with 14–15 °C higher outlet water temperature.

Geo-materials may present varying mechanical properties under different stress paths, especially for tunnel excavation, which is typically characterized by the decreased radial stress and increased axial stress during the complex loading and unloading process. This study carried out a comparative analysis between the loading and unloading model testing, which was then combined with PFC2D simulation, aiming to reveal the fracture propagation pattern, microscopic stress and force chain distribution of the rock mass surrounding the tunnel. Comparisons of extents and development of tensile strain between loading and unloading testing results were made. The overall stability, the integrity of rock mass, and the failure pattern transition under loading and unloading processes were systematically examined. In addition, for the two unloading cases with different vertical stresses imposed, the failure patterns were both identified as the collapse of the V − shaped extruded sidewall, due to the coupling of the shear failure and the vertical tensile failure in the sidewall wedge.

After approximately 15 years of service, the splined end of one of the screws of a twin screw extruder used in a polymer processing facility failed at the coupling with the gearbox. The failure resulted in damage to several elements including the coupling between the motor and main gearbox and the auxiliary motor. Metal particles obstructed a screen pack and were found on downstream equipment. The failure analysis conducted indicates the shaft of the screw fractured under primarily high cycle low stress fatigue under rotating-bending load conditions, associated with shaft misalignment at the coupling with the gearbox.

The flexural strengths of composite materials composed of polypropylene reinforced with cotton fibers recycled from textile waste are presented. Materials with and without coupling agents were prep...

Through the adiabatic temperature rise experiment, the adiabatic temperature rise of concrete with hydration time was recorded. Based on the maturity degree theory, the relationship between the hydration degree of the concrete and the equivalent age was determined. Then, the hydration degree prediction model of the concrete's early elastic modulus and tensile strength was established. The local temperature and humidity of the concrete were measured by the shrinkage experiment, and based on the capillary water tension theory, a temperature-humidity prediction model for the early shrinkage of the concrete was designed. According to the ratio of the creep deformation and elastic deformation of concrete which were obtained through the restraint ring experiment, a model for predicting the early creep coefficient of concrete was proposed. Based on the coupling effect of “hydration-temperature-humidity,” a prediction model of early cracking risk coefficient of concrete under multifield coupling was proposed. Finally, several groups of slab cracking frame experiments were carried out, and the cracking risk prediction results of concrete were consistent with the actual situation, which indicated the correctness of the early cracking risk prediction model of concrete.

The high-temperature syngas and molten slag droplets discharged from entrained-flow coal gasifiers contain a large amount of heat energy, which can be efficiently recovered by radiant syngas coolers (RSCs). However, it is hard to know the solidification degree of molten slag droplets at the outlet of an RSC during industrial operations. In this work, the industrial-scale RSC and molten slag droplet models are established to predict the solidification degree of slag droplets at the outlet of the RSC. Then, the effects of slag diameter, syngas flow field, slag initial temperature, slag porosity, and slag pore structure are investigated by numerical simulations, and residence time as well as complete solidification time are calculated by coupling of a discrete-phase model and a solidification model. The results indicate that as the slag droplet diameter increases, the residence time of the slag droplet shortens, but the complete solidification time increases. When the slag droplet diameter is greater than or equal to 3.0 mm, the complete solidification time is larger than the residence time, and the slag droplet cannot solidify completely at the outlet of the RSC. The solidification degree in the windward zone is greater than that in the leeward zone. Although the slag initial temperature has little effect on the solidification, a lower slag initial temperature is still conducive to a greater solidification degree. Additionally, the pore structure facilitates solidification, and the promoting effect of penetrated pores is more remarkable than that of closed pores. A larger porosity is also beneficial to accelerate the solidification of molten slag droplets and increase the solidification degree.

Wurster fluid bed coating is an effective way of manufacturing pharmaceutical pellets requiring specific characteristics such as high drug loading or enteric protection. The optimization of coating process can be demanding because it necessitates many time-consuming experiments. To reduce the need for experiments and prevent undesired agglomeration, a multi-scale model has been developed. On the device-scale, the model predicts the temperature, moisture content, and average coating thickness. On the micro-scale, the model estimates the evaporation time of a single sessile droplet. By coupling models at both length-scales, it is possible to evaluate droplet evaporation time as a function of process parameters and use it as a tool for process transfer between different production sites and equipment. The model was validated against existing production data. The predicted outlet air temperature was in good agreement, and most importantly, the predicted values of the evaporation time separated undesired agglomeration and successful coating regime.

Machines for milling asphalt concrete surfaces appeared on the highways of the Republic of Kazakhstan about ten years ago. Before that, the replacement of the old asphalt pavement took place under the deafening crack of jackhammers. Road cutters made it possible to replace this outdated technology with profiling of asphalt concrete surface. This type of work consists in removing the asphalt coating layer by cold milling. Typical characteristics of the road milling cutter: working speed of 5-7 m /min, sufficient power, traction and stability to ensure accurate maintenance of the working depth from 3.5 mm to 5 cm; automatic leveling system using a leveling beam or string; automatic control of the milling depth using guide slides; the ability to maintain a given transverse slope; auxiliary equipment for the selection of crushed material (asphalt granulate) at a given processing speed; the width of the working area of the milling strip is 2-4 m. Profiling of old asphalt pavement is an automatically controlled process of cold milling it to restore a given transverse and longitudinal profile, remove bumps, potholes, wear zones, as well as other coating defects, and as a result, obtain a surface that allows for the immediate start of movement or the laying of a fresh coating. Modern road cutters allow you to plan the old coating, texture its surface, giving it the lost coupling and noise protection properties, remove the old coating layer by layer (with an accuracy of up to mm) or immediately to the full depth, carefully open the places of laying underground pipelines and communication lines, release the old coating manholes and even level concrete floors in industrial premises. In this paper, this problem is supposed to be solved by presenting the road cutter as an automated road transport and technological manipulator operating in generalized technological coordinates for the repair of road surfaces with variable track age and due to the transition from elastic (power) to rigid (coordinate) closure of the technological scheme for milling track gauges.

Establishing relationship of elemental composition and mechanical property is a tremendous amount of work in superalloys. Here, machine learning coupled with high-throughput experiment is adopted to construct “composition-hardness” model in nickel-based superalloys. The hardness estimated from experiment agrees well with the predicted value. Furthermore, optimal composition of high-hardness superalloys is accurately predicted by simulated annealing algorithm. Subsequently, optimal composition is validated by Thermo-Calc software, further demonstrating the effectiveness of current approach. Here, a design strategy combined with high-throughput experiment and machine learning is proposed, which may be believed for accelerating the design of advanced materials with excellent performance.

In order to clarify the influence of residual stress on the stability of 2024-T3 friction stir welded(FSWed) integral stiffened panels with multi-welds, the ANSYS software was used to establish the finite element models of two typical multi-FSWed stiffened panels. The residual stresses of two typical multi-welded stiffened panels (Panel A and Panel B) were calculated respectively using the thermal-mechanical coupling method. And the buckling and post-buckling responses of the stiffened plates were analyzed. It is shown that the residual stress distribution of stiffened panel was affected by the welding sequence. The maximum residual stress of Panel A mainly appears on the right side of the stringer, and that of Panel B appears on the stringer that is welded later. The residual stress has a great influence on the stability of the welded stiffened panels. When the residual stress profiles are taken into consideration, the critical buckling loads of welded Panel A and Panel B will decrease 14.2% and 12.4% respectively.

The annular coaxial nozzle has good convergence and is widely used in laser melting deposition (LMD). In this paper, a new-type annular coaxial nozzle is developed, which can transform four-channel powder flow into annular distribution through the internal channel to obtain a more uniform distribution of powder in the circumferential direction. A three-dimensional computational fluid dynamics (CFD) numerical model is established. The dynamic behavior of Fe-based powder is described by discrete phase model (DPM). The influence of gas on powder particles is described by two-way turbulence coupling model. The convergence and transport characteristics of the nozzle are revealed. The accuracy of CFD model is verified by powder feeding experiment, and the deposition performance of powder nozzle is verified by single-track deposition experiment. The results show that the nozzle can provide stable powder feeding and excellent convergence characteristics. The powder flow is converged in a “Y” shape on the longitudinal section. The higher the powder concentration at the focal plane of the nozzle, the smaller the aspect ratio of single-track coating. The powder utilization rate of the nozzle can reach 76.97%.

Structural aerospace composite parts are generally cured in an autoclave. To achieve a homogeneous curing, computational fluid dynamics simulations have been increasingly used in thermal optimization. However, a transient computational fluid dynamics simulation of autoclave processing is resource intensive. This article outlines the concept of a quasi-transient coupling strategy to deal with the conjugate heat transfer problem inside an autoclave. In this approach, a computational fluid dynamics model is coupled with a finite element method (FEM) model through incorporating an empirical-based analytic equation, which describes the dependence of the heat transfer coefficient on pressure and temperature, into the computational fluid dynamics computations. This approach bridges the temporal disparities between the fluid and the solid, thus minimizing the global computing time. To validate this method, two simulation cases have been studied. In both cases, two different coupling computations are compared, namely a full-transient simulation as the reference computation and the introduced quasi-transient simulation. First, the quasi-transient coupling approach is implemented by performing the transient heat transfer analysis on a flat plate. The results indicate that this approach can predict accurate transient temperature fields, and the computational effort is reduced by up to 87%. Subsequently, this method is used in a real autoclave and validated by known experimental data. The simulation results are in good agreement with the experimental results, with a mean temperature error lower than 1.9°C. This indicates the capability and efficiency of this approach in solving a conjugate heat transfer problem for autoclave processing.

This study applies high rate forming technology to the manufacture of miniature parts and proposes a novel miniature parts bulk forming method, that is, laser shock micro-bulk forming (LSMBF). Through the numerical simulation and experimental research on 1100Al rod, the feasibility of manufacturing miniature parts using the LSMBF method is discussed. The similarities and differences of two simulation methods, namely, the smooth particle dynamics and finite element coupling (SPH-FE) and coupled Euler–Lagrangian (CEL) methods, were analyzed. Results show that the SPH-FE method is more consistent with the experiment and is more suitable for simulating the complex large deformation forming process of LSMBF than the CEL method. This study shows that the plastic deformation process of LSMBF is as follows. First, the upper end of the rod undergoes mushroom-shaped upsetting. Then, the bottom of the rod touches the micro die, and the upsetting phenomenon occurs. Finally, the micro-die is gradually filled. The plastic deformation of metal is related to the stress wave propagation and inertia effects. The main flow direction of the metal is axial, and the flow uniformity is fine. This study also shows that increasing the laser energy intensity is beneficial to improving the uniformity of the parts when impacting micro-die at high speed.

In order to study the vibration wearing regularity and the strength failure point of stator end windings before and after static rotor eccentricity, the three-dimensional electromagnetic forces and the subsequent mechanical responses are studied in this paper. The electromagnetic force, stress, and deformation on the end winding of the QFSN-600-2YHG turbo-generator are calculated by the finite element method (FEM) through an electromagnetic-structure coupling. The radial vibration characteristics of the winding are verified by experiments. It shows that the vibration wearing in the same layer is more serious than that between two neighboring layers. For different layers, the interphase coils endure a larger wearing risk than the innerphase coils. Inside the same phase, the last coil along the rotating direction has the highest risk of insulation wearing. The occurrence of static rotor eccentricity will significantly increase the electromagnetic forces and the vibration amplitudes on some coils. The end-phase coil which is close to the minimum air-gap point is the most dangerous one due to the lasting overstresses and the intensified deformations.

In order to solve gas and spontaneous combustion in high gassy and combustible coal seam, in this work, the hazard control of gas and spontaneous combustion was studied by numerical simulation and ...

The complex compositions and large shrinkage of concrete, as well as the strong constraints of the structures, often lead to prominent shrinkage cracking problems in modern concrete structures. This paper first introduces a multi-field (hydro–thermo–hygro–constraint) coupling model with the hydration degree of cementitious materials as the basic state parameter to estimate the shrinkage cracking risk of hardening concrete under coupling effects. Second, three new key technologies are illustrated: temperature rise inhibition, full-stage shrinkage compensation, and shrinkage reduction technologies. These technologies can efficiently reduce the thermal, autogenous, and drying shrinkages of concrete. Thereafter, a design process based on the theoretical model and key technologies is proposed to control the cracking risk index below the threshold value. Finally, two engineering application examples are provided that demonstrate that concrete shrinkage cracking can be significantly mitigated by adopting the proposed methods and technologies.

As compared with silica aerogels, alumina aerogels have excellent high-temperature stability, and hence, are regarded as a promising candidate for high-temperature thermal insulation materials. However, heat transfer mechanisms for such materials remain insufficiently explored. In this study, based on real material microstructures, an analytical thermal conductivity model for alumina aerogel-fiber-opacifier composites is developed via a modified parallel-series equivalent electrical circuit approach. The model takes into account solid, gaseous, and solid-gas coupling heat conduction in aerogels, solid heat conduction in both fibers and opacifier particles, and radiation in aerogels, fibers, and opacifier particles. The model is validated by comparing its predictions with measured thermal conductivity data. The model predictions reveal that there are two kinds of solid-gas coupling heat transfer mechanisms, which occur in the corner regions between interconnected secondary particles and in the slit regions between adjacent chains, respectively. Because of this coupling, the contribution of gaseous heat conduction is comparable to that of solid heat conduction and radiation of aerogels, fibers, and opacifier particles, which is well supported by experimentally measured data of thermal conductivity. The model is also used to analyze effects of various parameters on the thermal insulation performance of the composites, such as diameters and volume fractious of both fibers and opacifier particles.

In coal mines, under high in situ stress and strong mining activity, roadway surrounding rock commonly contains large amounts of larger fractures and microfractures. Along with the large deformation and continuous rheology of the soft rock roadway, the fractures in the surrounding rock are likely to be compressed and closed, forming undeveloped microfractures, which hinder conventional grouting support methods. Based on the fluid-solid coupling between slurry seepage and microfracture deformation, a theoretical model of microfracture grouting seepage is established. A program for the analysis and calculation of microfracture grouting is developed to quantitatively describe the variation in slurry seepage distance and fracture opening. Numerical experiments are carried out to study the grouting seepage of microfractures under different grouting pressures and fracture opening conditions, and the variation rules for the spatial distribution of fracture opening and slurry seepage distance during grouting pressure are obtained. Fluid-solid coupling has a significant influence on grout seepage characteristics. The grouting pressure and the fracture opening changes are nonlinearly attenuated along the grout seepage direction.

Coal seam water injection is a critical measure for the prevention of coal-and-gas outbursts. However, the gas–solid–liquid coupling effect in front of the working face before and after water injection during coal mining is scarcely investigated. This issue was explored in this study by (a) numerical simulation of stress, gas pressure, and water saturability distribution as well as their coupling effect in front of the working face via the proposed multi-field coupling model run in the COMSOL software and (b) comparative analysis of the above parameters before and after water injection. During coal mining, stress in front of the working face first increased and then dropped to the initial value as the distance from the coal wall increased, while gas pressure exhibited a similar distribution pattern. After water injection, the stress distribution pattern remained almost unchanged, but the stress peak shifted forward, the stress relief zone broadened, while the gas pressure around the borehole dropped. In particular, the gas pressure in front of the borehole increased slightly at the beginning of water injection. As water was permanently injected, the gas pressure in front of the borehole decreased, while that around the borehole further decreased. Meanwhile, the water saturability of the coal seam around each borehole increased, with a ring-shaped distribution pattern. Due to the interaction of water injection among multiple boreholes, the contour lines of water saturability showed semi-circular distribution patterns around multiple boreholes.

The most important factor that ensures the joint work of reinforcement and concrete in reinforced concrete structures is the adhesion at the contact between them. It is achieved by gluing reinforcement with cement stone, friction between the surfaces of these materials, as well as engaging the protrusions on the surface of the rods. In road and civil construction in the manufacture of reinforced concrete structures is most used reinforcing steel sickle profile. Until the 1990s, traditional profile reinforcement was used, which differs significantly from the newer crescent-shaped reinforcement. An important feature of the interaction of reinforcement with concrete is the mutual displacement, as a result of which there may be a redistribution of forces. These areas are called reinforcement anchoring zones. Destructive processes develop within a layer of very small thickness (several millimeters). The redistribution of forces between concrete and reinforcement depends most on the deformation of the contact layer, rather than the size of the shell [2]. Virtually all reinforced concrete structures, especially road structures, are subjected to significant re-loading during operation, the impact of which on the joint work of concrete and reinforcement has been very little studied. This article investigates the features of the coupling of reinforcing bars of class A500C depending on the length of the anchoring under the action of repeated loads. It is established that the size of the concrete shell does not significantly affect the value of the ultimate destructive force of elongation of the reinforcing rod at a single load and significantly more affects the amount of displacement of the reinforcement. Repeated loads affect both the ultimate forces and the complete mutual displacements of the rods relative to the concrete shell.

From the perspective of spontaneous combustion control in coal mining, this study conducted a progressive axial loading test of broken coal using a self-designed multi-field coupling oxidation test system. The evolutionary characteristics of the bulking factor under different loading conditions of stress, stress–temperature, and stress–moisture were obtained. Subsequently, factors affecting the bulking properties of broken coal in the synchronous compression and deformation stage were analyzed theoretically using the four-particle accumulation model and Hertzian contact deformation principle. The research results are summarized as follows: (1) in the process of axial loading, the bulking factor of broken coal generally decreased, but showing three stages; (2) under the stress-moisture coupling effect, when the axial force was 0 kN and the external water content increased from 0 to 6.75%, the water wedge effect increased the bulking factor of broken coal by 2.17%; (3) under the stress-temperature coupling effect, when the axial force was 47.1 kN and the temperature increased from room temperature (23.3 °C) to 100 °C, the bulking factor of broken coal decreased by 5.08%; and (4) in the synchronous compression and deformation stage (at the axial stress of 94.2 kN), the theoretical analysis revealed that the bulking factor decreased gradually with increasing stress, temperature, and external water content, which was consistent with the test results. The abovementioned test results established the basic theory and provide practical support for subsequent recognition of the spontaneous combustion of confined coal.

Currently, for the design of building structures on railway transport, prestress is increasingly used, in particular with cable fittings. The performance of this type of reinforcement is largely determined by the coupling of reinforcement with concrete in the contact zone and the work of the end sections of the bent structures. However, in modern research and calculation devices, methods for solving this problem are mainly phenomenological in nature. Calculating the strength of reinforcement anchorage in concrete, clarifying the calculation of the width of cracks, determining the length of the transmission zone of stressed reinforcement, developing methods for controlling the quality of coupling at enterprises that manufacture prestress structures, and other practical tasks require the creation of a simplified calculation apparatus. This paper presents the results of experimental studies of cable armature coupling in prestress cylindrical samples (with indirect spiral armature) with registration of surface deformations without interfering with the contact of the armature with concrete, a method for determining the coupling characteristics is presented, which in the future will simplify the numerical simulation of the interaction of the armature with concrete and make changes to the calculated approaches for determining the length of the anchorage of reinforcement rods and the length of the zone of force transfer from the stressed armature to concrete.

A high-speed (HS) permanent magnet (PM) synchronous motor (HSPMSM) with a carbon fiber-reinforced plastic (CFRP) protective sleeve in the surface-mounted rotor was explored in this study. In view of retaining the PMs at HS operations, the high-strength CFRP sleeve was designed on the basis of a process that could be summarized as follows. First, a multi-physics analysis of the rotor was conducted. The requirements to the CFRP sleeve were obtained from electromagnetic analysis, loss analysis, heat flow coupling computational fluid dynamics analysis, structural analysis, and rotor dynamics analysis. Second, the CFRP sleeve was designed by theoretical analysis. From the results, the thickness values of the carbon fibers in the circumferential and helical directions were chosen to be 4 and 1 mm, respectively, while the helical angle of carbon fibers was chosen to be 70°. Then, a plate-shaped CFRP product and a cylindrical CFRP product were fabricated to verify the strength and stiffness of the CFRP sleeve. The performance test results show that the hoop strength and elastic modulus and the axial strength and elastic modulus of the plate-shaped CFRP products at 20 °C are 1963 MPa @ 156 GPa and 550 MPa @ 36 GPa, respectively. The hoop strain and axial strain of the cylindrical CFRP product under 35 MPa are about 3000 and 1900 μe, which meet the design requirements of the HSPMSM.

In order to ensure safe mining and reduce surface damage in shallow multi-seam mining, the failure characteristics of interburden strata with different coal pillars offset distances between pillars in the upper and lower seams, the distribution characteristics of stress concentration in coal pillars, and the development characteristics of stratum cracks and subsidence were investigated by physical and UDEC2D simulation. Meanwhile, the effect of different coal pillar offset distances on stress concentration of coal pillar and development of stratum cracks were studied. Based on those results, a formula for safe mining and reducing surface damage was established, which provided a theoretical basis for safe and environmentally friendly mining in shallow multi-seam. According to the results, the optimal coal pillar offset distance (the side to side horizontal distance of the upper and lower coal pillars) between the upper and lower coal seams was developed to reduce the stress concentration of coal pillars and surface damage. The results of this study have been applied in Ningtiaota coal mine and have achieved good results in safe and environmentally friendly mining.

With the increasing demand for higher-level functional nanodevices, there is a strong requirement for the fabrication of high-crystallinity composite nanowires, e.g., one-dimensional end-to-end different-diameter silver nanowires. However, these nanowires have been mostly assembled by end-to-end physicomechanical coupling, which causes gap junctions or loose connections between the nanowires, limiting their extensive application. In this study, one-dimensional different-diameter silver nanowires with well-controlled shapes and high yields were synthesized. This type of nanowire comprises a thick nanowire and a thin nanowire of uniform diameters. The thin nanowire epitaxially grows on the end surface of the thick nanowire. The connection between the thick and thin nanowires shows high-crystallinity with Ag{100} facets. With temperature approaching 150 °C, the cross-linking reaction of the PVP chains is gradually intensified. As a result, the cross-linked PVP chains, which are adsorbed on the side surface (Ag{100}) near the end of the nanowire, extend over the edge of the end, forming Ag{100} facets. This reduces the effective area of the Ag {111} facets on the end surfaces of the nanowires. Consequently, a thin nanowire grows from the remaining Ag{111} facets at the end of the existing nanowire, forming different-diameter silver nanowires. Moreover, the surface plasmon propagation along this nanowire shows distinctive performance compared with that of the conventional end-to-end mechanically coupled nanowires, indicating that these different-diameter nanowires have unique properties, which can lead to more significant applications.

Oil and gas pipeline accidents most frequently occur in output places and weld joints. Increased stress in weld joints can be explained by the presence of stress concentrators and residual welding stresses. Pipeline pressure testing can reduce the value of residual welding stresses. The article considers the method of calculating coefficients of stress concentration depending on the construction, geometrical dimensions and the type of tee welding joints. The authors calculated and proved that reinforcing tee joints by means of a coupling ring increases the number of welding joints and coefficient of stress concentration. The study theoretically proves the possibility of reducing residual stresses in tee joints choosing the right mode of pipeline pressure testing and defines the limits of changes in pipeline pressure testing which ensure plastic deformation of metal in welding joints alongside the elastic deformation of the main material of the tee joint.

Within this paper, a numerical study was performed, aiming to assess the influence of fiber orientation on the mechanical properties of tensile specimens, by using the finite element method. The specimen, designed according to ISO-527-2, is type 1BA and consists of a reinforced polyamide with 30% glass fiber (PA66 GF30). The specimens were extracted from 2 mm thickness plates, for which the fiber orientation tensor was determined using the dedicated Moldflow software for injection molding. The composite material was modelled using Digimat mean-field homogenization tool. The mechanical evaluation was performed in Ansys finite element software by coupling it with Digimat and thus considering the anisotropic behavior of the material. Different mapping procedures and mesh sizes for the Moldflow model and Ansys model were considered.

The paper presents new design solutions for the protection of monolithic frames of multi-storey buildings with flat floors from progressive collapse. At the same time, two variants of strengthening the support zones - the zones of coupling of the plate with the column, providing the perception of peak bending moments in the event of a sudden change in the force flows of the structural system caused by the removal of one of the supporting columns, are considered: the 1st variant-reinforcement with the use of metal insert plates, the 2nd variant - reinforcement with the use of support frames with inclined reinforcing rods. Numerical studies of a fragment of the considered monolithic frame of a building according to the primary design scheme for the effect of the design load and according to the secondary design scheme for the out-of-design impact show the effectiveness of the proposed design solutions for strengthening the interface zones of flat slabs with columns to protect the monolithic frames of buildings from progressive collapse. It is established that in the considered numerical example, the steel consumption when using the option of reinforcing the support zone with frames with inclined rods, other things being equal, is reduced to 46%.

The blades of a hydrokinetic turbine have a great impact on its performance due to they are the elements responsible for capturing the kinetic energy from water and transform it into rotational mechanical energy. In this work, numerical analyses on the performance of a multi-element blade section were developed. The lift and drag coefficients (CL and CD, respectively) of the hydrofoils with traditional and multi-element configurations were studied. For this purpose, 2D numerical analyses were conducted by using JavaFoil code. S805, S822, Eppler 420, Eppler 421, Eppler 422, Eppler 423, Eppler 857, Wortmann FX 74-CL5-140, Wortmann FX 74-CL5-140 MOD, Douglas/Liebeck LA203A, Selig S1210, Selig S1223 and UI-1720 profiles were tested. The results indicated that the Eppler 420 multi-element hydrofoil provided high efficiency to the turbine. This was attributed to its higher relationship between the maximum CL and CD (CLmax /CD), which was equal to 47.77, compared to that of the Selig S1223 profile (39.59) and other hydrofoils studied. Therefore, the final optimized blade section selected was an Eppler 420 multi-element hydrofoil with a flap chord length of 70% of that of the main profile. The hydrodynamic and structural designs of the optimized blade section were validated with detailed 3D numerical models, through ANSYs Fluent software. The fluid and structural domains were connected using one-way coupling. The influence of the blade geometry and the operational parameters on the stresses supported by the blades were found by analyzing the fluid-structure interaction. From the numerical analyses conducted, it was observed that the blades did not exhibit structural fails. In this regard, the multi-element hydrofoil might be used for the design of a horizontal-axis hydrokinetic turbine with a high efficiency.